Changes:
- added config for NEW_CTX_SWITCH
- used new context on c906 sched switch routine
- update _rt_hw_stack_init to fit into NEW_CTX_SWITCH
- separated vector ctx from the generic

Signed-off-by: Shell <[email protected]>

These changes are designed to standardize the memory management across
'virt64' and 'c906', ensuring efficient handling of address spaces and
page tables.

Changes:
- Creation of ASID management files (`asid.c`) for both 'c906' and
  'virt64' architectures, which is essential for maintaining stability.
- Extensive updates to the MMU configuration and handling in `mmu.c` and `mmu.h` files.
- Addition of functions to manage ASID allocation and switching of page tables.
- For c906, accommodated the early memory setup to the one from virt64.

Signed-off-by: Shell <[email protected]>

This patch aims to unify the two currently separated RISC-V 64-bit
architecture ports, 'virt64' and 'c906', into a single generic
'common64' port. The changes include renaming files and updating
includes to use a unified 'interrupt.h' header, as well as making
adjustments to IO and trap handling to be more consistent between the
two architectures.

Changes:
- Renamed 'rt_interrupt.h' to 'interrupt.h' and updated includes accordingly.
- Unified IO register access functions in 'riscv_io.h'.
- Added 'opcode.h' for portable assembly support.
- Updated 'plic.c' and 'plic.h' to handle interrupts in a unified manner.
- Modified 'trap.c' to handle exceptions and interrupts consistently for 'rv64'.

Signed-off-by: Shell <[email protected]>

This patch consolidates the separated architecture-specific code for
rv64 (virt64 and c906) under a more unified approach. The changes
aim to enhance maintainability and code reuse, reducing duplication
between these two architectures while adding small improvements in
porting compatibility.

Changes:
- Modified build scripts (SConscript) for both virt64 and c906 to
  remove ASID and vector dependencies when not required.
- Updated c906's sbi.c and sbi.h to use standard integer types
  (uint32_t) and include the missing <stdint.h> header.
- Unified inline function declaration for `sbi_call` across both
  c906 and virt64 using `rt_inline`.
- Disabled FPU and vector in c906's startup assembly file, aligning it
  with the virt64 handling.
- Corrected syscall handler type definitions in c906 for consistency.

Signed-off-by: Shell <[email protected]>